Abuja , Nigeria -LRB- CNN -RRB- -- More than 70 members of the Islamist extremist group Boko Haram have been killed during a Nigerian military operation in the northeastern state of Borno , an Army spokesman told CNN on Friday .

The military `` remains on the offensive , '' according to Brig. Gen. Ibrahim Attahiru , who said the operation started Thursday and continued into the next day .

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This was n't the only clash between Boko Haram and Nigerian troops of late .

Suspected members of the extremist group around 5:30 p.m. Wednesday -LRB- 12:30 p.m. ET -RRB- attacked a military checkpoint in Damaturu , Nigeria 's Joint Task Force reported in a statement . Also in northern Nigeria , Damaturu is the capital of Yobe state .

Special operations troops responded , waging `` a fierce encounter with the terrorists in various parts of Damaturu ... for several hours , '' according to the Joint Task Force .

By the time that fighting was over , 21 suspected Boko Haram fighters were dead , the government group reported . Three vehicles were recovered , as were assault rifles , a rocket-propelled grenade , improvised explosive devices and 709 rounds of ammunition .

The military did not provide any information on its casualties .

`` Law abiding citizens are enjoined to remain calm as the 3 Division Special Operation Battalion is on top of the situation , '' the Joint Task Force said , noting a 24-hour curfew was imposed throughout the state . `` Any credible information should be passed promptly to security agencies for necessary action . ''

Last May , President Goodluck Jonathan put three states in the region under a state of emergency , giving Nigerian forces wide latitude in fighting the group , which human rights organizations say has killed more than 3,000 people since 2009 .

Boko Haram , which means `` Western education is sacrilege '' in the Hausa-Fulani language , seeks to impose a strict version of Sharia law across northeastern Nigeria , if not the entire country .

The group has attacked various targets in the West African nation since its formation in the late 1990s , according to the U.S. National Counterterrorism Center , including killing and kidnapping Westerners , and bombing schools and churches .

Hundreds of its members , including its leader Mohammed Yusuf , died in July 2009 clashes with government forces . But the group did not stay down for long , and has remained an active and violent force in Nigeria .

In August , its militants allegedly went into a mosque in Borno state and killed 44 worshipers . The group released a video boasting that it was growing stronger .

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CNN 's Vlad Duthiers reported from Nigeria , CNN 's Greg Botelho wrote this story from Atlanta . CNN 's Nana Karikari-apau contributed to this report .

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The military kills more than 70 Boko Haram members in an operation in Borno state

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They also fend off an attack on a military checkpoint in Yobe state 's capital

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21 suspected Boko Haram members die in fighting there

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Boko Haram seeks to impose a strict version of Sharia law across northeastern Nigeria